Part 7: Best Practices for Building a Resilient OT Security Program

In previous parts of this series, we have followed the OT security journey from business drivers and use cases through threats, architecture, roles, and the evolving solution landscape. We will now direct our attention to executing our plan.

What is the most effective method for developing and maintaining a comprehensive OT security program that can be implemented across multiple sites, systems, and stakeholders?

What distinguishes organizations that merely implement tools from those that integrate security into the very fabric of their operations?

This installment presents proven best practices that help organizations transition from reactive controls to a mature, risk-based, and resilient OT security posture.

1. Start with a Risk-Based Strategy, Not Technology

The temptation to “buy a tool and plug it in” is strong, but achieving real success starts with understanding risk. Before the deployment of any product or framework:

• Identify your most critical OT assets and processes
• Understand potential impact: downtime, safety incidents, compliance violations
• Map threats to real-world business consequences

This risk-first approach ensures that security investments align with operational priorities, not just security theory.

Best practice: To map business risks to controls, consider using frameworks such as NIST CSF, MITRE ATT&CK for ICS, or IEC 62443.

2. Build on Visibility and Inventory

Security programs must have a comprehensive understanding of the assets they are protecting. However, undocumented assets, shadow systems, and legacy devices are the norm in the OT environment.

First, utilize asset discovery tools that are passive and protocol-aware to establish a dynamic inventory that supports:

• Device identification and classification
• Firmware version tracking
• Vulnerability exposure mapping

Ensure that visibility is maintained continuously, rather than as a one-time project.

Best practice: Initiate the process with a limited pilot (e.g., one plant or line), and subsequently expand.

3. Segment and Contain Risk Zones

Flat OT networks are similar to open-plan offices in that they are both convenient but risky. Network segmentation, both logical and physical, is foundational.

• Define zones (e.g., enterprise, DMZ, control, field)
• Use conduits (firewalls, data diodes) to manage flows tightly
• Prevent lateral movement from IT into OT, and within OT

Best practice: Avoiding a “one big firewall” approach is advisable. Employ defense-in-depth with micro-segmentation when feasible.

4. Establish Secure Remote Access and Access Governance

While remote access is often necessary, it is also one of the most exploited OT attack vectors.

• Enforce least privilege access
• Use jump hosts, MFA, session recording, and approval workflows
• Apply strict access expiration and vendor management policies

Best practice: It is essential to separate control plane access, such as remote diagnostics, from data plane flows.

5. Integrate IT and OT Security Operations

Many organizations categorize OT incidents as “engineering issues” and IT threats as “security issues.” This division can lead to delays, blind spots, and coordination failures. Instead:

• Train your IT SOC to understand OT alerts and protocols
• Create joint playbooks for OT incident response
• Ensure forensic data (e.g., PCAPs, log trails) is available to both teams
• Align on escalation paths and responsibilities

Best practice: Consider a unified or federated SOC/NOC model with OT expertise.

6. Embed Governance, KPIs, and Continuous Improvement

A strong start can fade without sustainable governance. To ensure long-term resilience, it is essential to implement the following strategies:

• Clear policies and standards (based on IEC 62443 or similar)
• Assigned accountability (plant-level and central roles)
• Regular risk reviews, compliance checks, and audits
• KPIs that combine security (e.g., threat detection time) and operational impact (e.g., downtime avoided)

Best practice: It is essential to link OT security KPIs to business outcomes, rather than solely focusing on technical metrics.

7. Start Small, Scale Smart

Attempting to address all aspects simultaneously can result in delays or complications. Instead:

• Begin with a high-value use case (e.g., visibility, remote access, or compliance gap)
• Choose a pilot site or region with strong stakeholder buy-in
• Show early wins and use them to secure further investment
• Build a reference architecture that can scale

Best practice: It is essential to approach OT security with a mindset that recognizes it as an ongoing journey rather than a finite project.

Conclusion: From Compliance to Competitive Advantage

A successful OT security program is more than a protection measure; it is an enabler. It enables factories to modernize safely, utilities to operate more reliably, and transport systems to remain operational even under threat.

Organizations that prioritize OT security as a fundamental capability, integrated into their design, operations, and innovation processes, are at the forefront of this field.

While technology, architecture, and tools are essential, people, processes, and partners ultimately determine success.

Up Next: The Future of OT Security – Trends, AI, and Regulation

In the final part of this series, we will look ahead. What are the prospects for OT security? What impact will artificial intelligence, increasing regulation, and the convergence of IT, OT, and IoT have on the future of this landscape?

What measures can be taken to ensure that your security program is prepared for tomorrow’s challenges and opportunities?